The thermodynamic argument for SETI.

Rather curious...

Rich

---------------

http://www.upscale.utoronto.ca/Gener...oleThermo.html

[...]

Sentient Beings

Hawking and Bekenstein did much of the above work on the thermodynamics of black
holes and the universe. In this section we consider a speculation for which I
must take the blame.

Reference: D. Harrison, "Entropy and the Number of Sentient Beings in the
Universe," Speculations in Science and Technology 5 (1982) 43.

First, we must think a bit about information.

The search for extra-terrestrial life has concentrated on scanning the universe
for radio waves and trying to see if the patterns of the radiation could contain
evidence of intelligence. When the pulsars, the radio sources that send blips at
highly regular intervals, were first discovered some people got very excited and
thought perhaps the search had yielded a positive result; now we believe that
the pulsars are the radiation from rapidly rotating neutron stars.

If we receive a radio transmission that is just static, there is very little
information in it. The information content of a signal depends on that signal
being ordered, not random. Thus if the extra-terrestrial beings are sending
information to us in radio waves the signal will be ordered in some way.

Thus, information must have low entropy. You may recall that earlier we
mentioned the negentropy, which is the negative of the entropy: it measures the
amount of order in a system. People who work in information theory customarily
think about the negentropy.

We are, hopefully, acquiring information about the world, ourselves, our friends
all the time. Thus we are creating negentropy in our mental system.

Now, the Second Law of Thermodynamics says that the entropy is increasing. This
is a sort of strange law for a physicist: it says that the entropy is never
conserved. This is as opposed to the types of laws that we are used to, which
talk about conditions under which things are conserved.

You will also recall that Quantum Mechanics seems to say that there are no
observers in the universe, only participators. Thus the universe is in some
sense brought into being by communicating participators acquiring information
about it (and vice versa).

What if the Second Law of Thermodynamics is not quite complete as stated? My
speculation is that it could be extended to read:

The rate of production of physical entropy by the universe equals the rate of
production of negentropy by sentient beings in the universe.

Now we have a conservation law.

However, the total physical entropy of the universe is increasing, and we can
calculate the rate of that increase. If we could calculate the rate at which a
typical human-like creature acquires information throughout its lifetime, then a
simple division will allow us to calculate the number of such sentient beings
there are in the universe.

To guess at the rate at which we produce negentropy we take our memory system to
be essentially digital, with each of the 1014 synapses in our brain in either an
on or off state. The combinations of synapse states are just the same as the
combinations of black marble-white marble states that I insisted we think about
when we discussed entropy in an earlier class. So, just as always, we count the
number of combinations to calculate the entropy, whose negative is the negentropy.

We assume evolution is efficient, so the memory store is full after 100 years.

The result of dividing this rate of negentropy production into the rate at which
physical entropy is being produced by our expanding universe is a number on the
order of 10102 sentient human-like beings in the universe. To put this number
into context, there are on the order of 1080 protons plus neutrons in the universe.

So, perhaps this is a failed speculation. Other alternatives include:

* Neutrons, protons, etc. are sentient.
* The human memory system contains a great deal more potential that we have
allowed for.
* We have not included the negentropy production due to the communication
that occurs between sentient beings.
* We, along with Hawking and Bekenstein, have calculated the rate of
physical entropy production in the universe using equilibrium thermodynamics. A
self-organising universe with negentropy production through dissipative
structures makes our calculation of the rate of physical entropy production
incorrect.